CHAPTER XXI.
OF THE RELATIONS OF THE SEISMIC FOCI OF THE ITALIAN PENINSULA, AND THE GENERAL RELATIONS OF THE SEISMIC BANDS OF THE MEDITERRANEAN BASIN.
Humboldt has remarked, of the Mexican and South American earthquakes, as well as of those of the United States, that in the course of time, they seem to change their centres of effort, as evidenced by the boundaries of disturbance becoming enlarged in one direction and retracted in the opposite. Such is also the fact in the Italian peninsula. If the Map C be examined, and if the British Association Earthquake Catalogue, or, still better, Perrey's Monograph Catalogue of the Italian Earthquakes, be collated, it will be found that the locus of their numerous focal centres follows generally the lines of the great ridges of the Apennines, but the distribution is not uniform. From the toe of Calabria, northward, to the extremity of Gargano, the line of foci is nowhere quite interrupted, along the north and south Apennine, but the seismic centres cluster thickest, round that of the great shock of 1783, (between the Gulfs of St. Euphemia and Squillace); again, between Lagonegro and Melfi; and at the northern end between Foggia and the point of Gargano.
This locus line of foci bifurcates, or rather is crossed,
